If I create a varaible definition like this:
variable "aws_ecs_config" {
type = object({
cpu = number
memory = number
ecs_image_address = string
})
logs = {
type = object({
group = string
region = string
stream_prefix = string
})
}
}
How can I reuse that definition across multiple modules without copy-pasting?
It is not possible to re-use variable declarations in Terraform. If variables in different modules will have the same type, that type must be repeated in each module.
Terraform has a structural type system rather than a nominal type system, so types themselves are not named and instead are matched/constrained by their form. When passing values between modules, we can use type constraints to create conventions between a family of related modules, but there is no mechanism to define a type (or declare a variable) in one place and reuse it in other places.
Terraform's type constraint mechanism considers any object with at least the attributes in the type constraint to be valid, so it's not necessary to define an exhaustive object type every time.
For example, if you define a variable with the following type:
object({
name = string
})
The following object value is acceptable for that type constraint, because it has a name attribute of the correct type regardless of any other attributes it defines:
{
name = "foo"
other = "bar"
}
For that reason, it can be better to limit the variable declaration in each module to only the subset of attributes that particular module actually requires, which reduces the coupling between the modules: they only need to be compatible to the extent that their attribute names overlap, and don't need to directly bind to one another.